Heat-meltable fluororesin for injection molding

Abstract

To provide a heat-meltable fluororesin for injection molding which contains a copolymer containing TFE and PEVE and which has excellent properties such as injection moldability (mold fillability), low temperature moldability, mechanical strength (toughness), flex resistance, solvent resistance, and the like, and to provide an injection molded article containing this heat-meltable fluororesin. A heat-meltable fluororesin for injection molding, containing a copolymer containing 88.7 mass% or more and less than 90.9 mass% of tetrafluoroethylene (TFE) and more than 9.1 mass% and no more than 11.3 mass% of perfluoro(ethyl vinyl ether) (PEVE), wherein the copolymer has a melt flow rate at 372°C in the range of 25 to 50 g / 10 min and has 50 or fewer unstable terminal groups per 1 x 106 carbon atoms in the copolymer.

Description

AP0444-W001TITLE OF INVENTION HEAT-MELTABLE FLUORORESIN FOR INJECTION MOLDING CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of Japanese Patent Application No. 2025-016967 filed February 4, 2025, and claims the benefit of priority of Japanese Patent Application No. 2025-204030 filed November 26, 2025, the disclosures of which are incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a heat-meltable fluororesin, and more specifically to a heat-meltable fluororesin which has properties suitable for injection molding and which can be molded into an injection molded article having excellent mechanical strength and flex resistance while also having low-temperature moldability.BACKGROUND ART

[0003] A copolymer (PFA) of tetrafluoroethylene (TFE) and perfluoro(alkyl vinyl ether) (PAVE) has excellent properties similar to TFE, such as heat resistance, chemical resistance, and the like, as well as thermal melting properties, and therefore is used in melt molding such as melt extrusion molding, injection molding, blow molding, melt compression molding, and the like. The obtained molded products are used as pipes and joints for transporting chemical solutions, storage containers, and the like in semiconductor manufacturing processes, chemical plants, and the like.

[0004] Of the aforementioned molding methods, injection molding is capable of molding products having complex shapes such as joints and the like, and generally uses PFA having a high melt flow rate (MFR). For example, the following Patent Document 1 describes a molding material made of PFA having an MFR of 14.8 to 50 g / 10 min, containing 4 mass% or more of PAVE units, having a melting point of 295°C or higher, and having 50 or less unstable terminal groups per 1 xio6carbon atoms in the copolymer, and describes that,AP0444-W001perfluoro(propyl vinyl ether) (PPVE) is preferably used as a copolymerization component in the aforementioned molding material, from the viewpoint of heat resistance, and the like, but although the aforementioned Patent Document 1 lists perfluoro(ethyl vinyl ether) (PEVE) as one of the PAVE units that is a copolymerization component, Patent Document 1 does not specifically mention PFA containing PEVE as a copolymerization component.

[0005] On the other hand, Patent Document 2 listed below describes a TFE / PEVE copolymer that contains at least 3 mass% PEVE and has a melt viscosity of 25 x 103Pa s or less at 372°C, and when the amount of PEVE exceeds 10 mass%, the melt viscosity exceeds 25 x 103Pa s at 372°C. Patent Document 2 also describes that this TFE / PEVE copolymer has excellent melt processability, and that molded articles obtained therefrom have high toughness and long flexural life.

[0006] Furthermore, Patent Document 3 listed below describes a copolymer containing 4.4 to 6.2 mass% of PEVE, having an MFR of 0.8 to 4.0 g / 10 min, and having 20 or fewer unstable terminal groups per 106main chain carbon atoms of the copolymer.CITATION LIST PATENT LITERATURE

[0007] Patent Document 1 : Patent No. 4228917Patent Document 2: Patent No. 3519411Patent Document 3: Patent No. 7364989SUMMARY OF INVENTION TECHNICAL PROBLEM

[0008] The aforementioned Patent Document 2 states that the TFE / PEVE copolymer is melt-processable, but a wide range of melt viscosity is described, and it is unclear what range of PFA will exhibit suitable injection moldability and provide an injection-molded article that satisfies all of the requirements for low-temperature moldability, mechanical strength (toughness), flex resistance, and solvent resistance.AP0444-W001

[0009] The aforementioned Patent Document 3 describes that the PFA is a copolymer that can be molded by melt extrusion molding or the like into sheets or films, such as release films or processing sheets used in hot press molding. However, the PFA disclosed in Patent Document 3 has a low MFR, inhibiting use for injection molding, and thus a suitable injection molded article cannot be obtained.

[0010] In general, when PEVE is used as a copolymerization component, compared with when PPVE is used as a copolymerization component, the copolymerization component is incorporated more uniformly and in larger quantities into the molecular chain, the reaction rate with TFE is faster, and the polymerization reaction is easier to control. In addition, PEVE has the advantage that the low melting point allows low-temperature molding and reduces resin damage.

[0011] Furthermore, the properties required for a heat-meltable fluororesin for injection molding, such as injection moldability, mechanical strength, flex resistance, and solvent resistance of the obtained injection molded article are affected by the amount of PEVE, which is a copolymerization component, the MFR value, and the like. For example, increasing the PEVE content improves the injection moldability and flex resistance, but reduces toughness such as breaking strain. Therefore, preparing a heat-meltable fluororesin for injection molding having all the properties in a good balance is difficult.

[0012] Accordingly, an object of the present invention is to provide a heat-meltable fluororesin for injection molding which includes a copolymer containing TFE and PEVE and which has excellent properties such as injection moldability, low-temperature moldability, mechanical strength (toughness), flex resistance, and solvent resistance, and an injection molded article containing this heat-meltable fluororesin.AP0444-W001SOLUTION TO PROBLEM

[0013] The present invention provides a heat-meltable fluororesin for injection molding containing a copolymer containing 88.7 mass% or more and less than 90.9 mass% tetrafluoroethylene (TFE) and more than 9.1 mass% and no more than 11.3 mass% perfluoro(ethyl vinyl ether) (PEVE), wherein the copolymer has a melt flow rate at 372°C in a range of 25 to 50 g / 10 min and has 50 or fewer unstable terminal groups per 1 x 106carbon atoms in the copolymer.

[0014] The heat-meltable fluororesin for injection molding of the present invention preferably has a melting point of 280°C or lower and a crystallization temperature of 260°C or lower, as measured by a differential scanning calorimeter.

[0015] The present invention also provides an injection molded article containing the aforementioned heat-meltable fluororesin for injection molding. The injection molded article is preferably any one of a tube, a bottle, a joint, a valve, or a pipe.ADVANTAGEOUS EFFECT

[0016] The heat-meltable fluororesin for injection molding of the present invention can have a good balance of all properties required of a heat-meltable fluororesin for injection molding, such as injection moldability, low-temperature moldability, mechanical strength (toughness) of the obtained injection molded article, flex resistance, solvent resistance, and the like, by adjusting the amounts of TFE units and PEVE units, the MFR, and the number of functional groups.

[0017] In other words, as is clear from the results of the examples described later, the resin has mold filling properties indicated by the zero-shear viscosity (injection moldability where the molten resin reliably reaches every corner of the mold during injection molding, allowing for stable molding of an injection-molded article conforming to the mold), and can be injection molded at relatively low temperatures, allowing for injection molding without causing thermal decomposition of the resin. Furthermore, the obtained injectionAP0444-W001molded article has excellent mechanical strength (toughness) as indicated by the breaking strain and toughness measured by a tensile test, and also has flex resistance as indicated by a flex life test, and solvent resistance as indicated by the rate of weight change obtained by an isopropanol immersion test, and all of these properties are well-balanced (Examples 1 to 4).

[0018] In contrast, at least one of the aforementioned properties cannot be satisfied by a heat-meltable fluororesin containing a copolymer that does not satisfy any one of the amount of TFE units and PEVE units, and the MFR (Comparative Examples 1 to 8).DESCRIPTION OF EMBODIMENTS

[0019] A first important feature of the heat-meltable fluororesin of the present invention is that it is composed of a TFE / PEVE copolymer containing 88.7 mass% or more and less than 90.9 mass%, particularly in the range of 89.2 to 90.8 mass%, and particularly preferably in the range of 89.4 to 90.7 mass%, of TFE units, and more than 9.1 mass% and 11.3 mass% or less, particularly in the range of 9.2 to 10.8 mass%, and particularly preferably in the range of 9.3 to 10.6 mass% of PEVE units.

[0020] In other words, when the amount of TFE units is higher and the amount of PEVE units is less than the above range, the melting point and crystallization temperature will be higher than when the amounts are within the above ranges, and thus the low-temperature moldability and flex resistance are reduced. On the other hand, when the amount of TFE units is lower and the amount of PEVE units is higher than the above range, the breaking strain and toughness in a tensile test will tend to decrease, and the mechanical strength (toughness) tends to decrease, as compared with a case where the TFE units are within the above range.

[0021] An injection molded article having a favorable balance of properties that are affected by the amount of PEVE, such as heat resistance, mechanical strength, and flex resistance, can be molded by adjusting the amount of PEVE in the heat-meltable fluororesin of the present invention to a specific range.AP0444-W001

[0022] A second important feature of the heat-meltable fluororesin of the present invention is that the MFR (based on ASTM D1238) measured under a load of 5 kg and at a measurement temperature of 372°C is in a range of 25 to 50 g / 10 min. The lower limit of the MFR is preferably 26 g / 10 min or more, more preferably 27 g / 10 min or more, even more preferably 28 g / 10 min or more, even more preferably 29 g / 10 min or more, and most preferably 30 g / 10 min or more, and the upper limit of the MFR is preferably 45 g / 10 min or less, more preferably 40 g / 10 min or less.

[0023] In other words, when the MFR is smaller than the aforementioned range, the mold filling property during injection molding will be inferior, so molding an injection molded article having excellent dimensional stability to match the mold will be difficult, as compared with the case where the MFR is within the aforementioned range. On the other hand, if the MFR is greater than the above range, the solvent resistance will be inferior to the case of being in the above range.

[0024] With the heat-meltable fluororesin of the present invention, even those resins having a high MFR suitable for injection molding can be made to satisfy all the performance properties affected by the MFR, such as the mold filling property expressed by the zero shear viscosity described later, the flex resistance expressed by the MIT flex life value, and the like, in a well-balanced manner, by adjusting the MFR to the aforementioned range.

[0025] A third important feature of the heat-meltable fluororesin of the present invention is that the number of unstable terminal groups per 1 x 106carbon atoms in the copolymer is not more than 50, especially not more than 10.

[0026] In other words, unstable terminal groups such as -CH2OH terminal groups, -CONH2 terminal groups, and -OOF terminal groups present in the copolymer are chemically reactive and thermally unstable, and thus there is a possibility that corrosive HF gas can be generated. The heat-meltable fluororesin of the present invention has a reduced number of such unstableAP0444-W001terminal groups, and thus the occurrence of corrosion of an injection molding die is remarkably reduced. In addition, the fluorination treatment described below for reducing the number of unstable terminal groups makes the terminal of the TFE / PEVE copolymer a -CF3 group, and thus the solvent resistance and the like can be further improved.

[0027] The heat-meltable fluororesin of the present invention can satisfy the following properties by adjusting the amount of comonomer and MFR of the TFE / PEVE copolymer to the aforementioned ranges.

[0028] In other words, the heat-meltable fluororesin of the present invention is adjusted so that the melting point (Tm) is 280°C or lower and the crystallization temperature (Tc) is 260°C or lower, as measured by a differential scanning calorimeter (DSC) by the method described below. This enables injection molding at a relatively low temperature in the range of 300 to 350°C and injection molding can be performed without causing thermal decomposition of the resin.

[0029] In the heat-meltable fluororesin of the present invention, the lower limit of the zero shear viscosity is 1000 Pa s or more, preferably 1200 Pa s or more, more preferably 1400 Pa s or more, and the upper limit of the zero shear viscosity is 2300 Pa s or less, preferably 2200 Pa s or less, more preferably 2100 Pa s or less, and even more preferably 2000 Pa s or less.

[0030] In other words, when the zero shear viscosity is lower than the aforementioned range, the mechanical strength and solvent resistance of the obtained injection molded article may be inferior, as compared with the case where the zero shear viscosity is within the aforementioned range, and when the zero shear viscosity is higher than the aforementioned range, the mold filling property may be inferior as compared with the case where the zero shear viscosity is within the aforementioned range, but with the heat-meltable fluororesin of the present invention, the mold filling property of the molten resin at the time of injection molding is excellent, so the injection molded article canAP0444-W001be stably molded to match the mold, and the mechanical strength and solvent resistance of the obtained injection molded article will also be favorable.

[0031] The heat-meltable fluororesin of the present invention has a breaking strain of 290% or more and a toughness of 55 MJ / m3or more, both of which are above certain values, as determined from a stress-strain curve obtained by a tensile test (based on ASTM D3307) described below, and thus has excellent toughness.

[0032] The breaking strain and toughness can be measured by a conventional tensile test. Specifically, a tensile test is carried out based on the method described in the Examples below, and the stress-strain curve obtained is used for calculation.

[0033] Furthermore, the heat-meltable fluororesin of the present invention has an MIT flex life value (FL value) of 110000 times or more, as measured by the method described later, and thus can be suitably used also in applications requiring flex resistance, such as tubes.

[0034] The FL value indicates the resistance to repeated bending, and can be generally improved by increasing the melt viscosity or increasing the amount of the copolymer component, but in the heat-meltable fluororesin of the present invention, the FL value is adjusted to the aforementioned value or more while balancing with other performance properties such as moldability and heat resistance.

[0035] Furthermore, the heat-meltable fluororesin of the present invention preferably has a small isopropanol (I PA) weight change rate (%) of less than 0.1% as measured by the method described later and thus can be molded into an injection molded article that is not affected by chemical solutions.

[0036] The heat-meltable fluororesin for injection molding of the present invention contains a copolymer containing TFE units and PEVE units in the aforementioned amounts, and is preferably a TFE / PEVE binary copolymer, but may contain other additional non-functional orfunctional fluorinated comonomers,AP0444-W001on condition that the TFE units and the PEVE units are contained in the aforementioned ranges.

[0037] Other additional non-functional fluorinated comonomers that may be included can include, for example, fluoroolefins (other than TFE) having 2 to 8 carbon atoms and fluorinated alkyl vinyl ethers where the alkyl group contains 1 or 3 to 5 carbon atoms. Preferred examples of fluoroolefins include hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE).

[0038] The heat-meltable fluororesin of the present invention (TFE / PEVE copolymer) can be prepared by a conventionally known polymerization method such as suspension polymerization, solution polymerization, emulsion polymerization, bulk polymerization, and the like.

[0039] Furthermore, during polymerization, the conditions such as temperature, pressure, stirring speed, and the like, as well as the polymerization initiator, surfactant, chain transfer agent, solvent, and the like, may be as conventionally known and used in accordance with known formulations. The surfactant (emulsifier) used during emulsion polymerization can be, for example, the fluoroether acids described in Japanese Patent No.5588679, hydrocarbon surfactants described in Japanese Patent No.6109073, and the like. In each polymerization method, the MFR can be adjusted to a desired value by adjusting the type and amount of the polymerization initiator, chain transfer agent, and the like.

[0040] The TFE / PEVE copolymer obtained by polymerization is preferably subjected to a fluorination treatment, whereby the number of unstable terminal groups described above can be reduced. The fluorination treatment can be carried out by the method described in Japanese Unexamined Patent Application No. S62-104822.

[0041] In particular, although not a limitation, the TFE / PEVE copolymers are brought into contact with a fluoride gas at a temperature of 50°C to 250°C, preferably up to 200°C, at atmospheric pressure or 0 to 1 MPa (gauge) pressure for 1 to 20 hours. The fluorine gas to be used can be pure fluorineAP0444-W001gas, but from the viewpoint of safety, fluorine gas diluted to 2 to 50% by volume with an inert gas such as nitrogen gas, helium gas, argon gas, or the like is preferably used. The shape of the TFE / PEVE copolymer to be contacted is not particularly limited, and may be any shape such as powder shape, pellet shape, flake shape, or the like.

[0042] The heat-meltable fluororesin for injection molding of the present invention may be blended with other thermoplastic resins such as polyolefins, polyesters, polyamides, and the like, styrene-based thermoplastic elastomers, or thermosetting resins such as phenol resins, epoxy resins, and the like, as long as the properties of the heat-meltable fluororesin of the present invention are in good balance and are not impaired during injection molding.

[0043] Furthermore, PFA and / or PTFE other than the TFE / PEVE copolymer of the present invention may be included. Examples of PFA include TFE and PAVE having 4 or fewer carbon atoms, or in other words, perfluoro(methyl vinyl ether) (PMVE), perfluoro(propyl vinyl ether) (PPVE), and perfluoro(butyl vinyl ether) (PBVE).

[0044] Furthermore, various additives such as antioxidants, ultraviolet stabilizers, crosslinking agents, lubricants, plasticizers, thickeners, fillers, pigments, dyes, flame retardants, antistatic agents, and the like may be added as needed within a range that does not impair the properties of the heat-meltable fluororesin of the present invention.

[0045] As described above, the heat-meltable fluororesin of the present invention has excellent mold filling properties and has a reduced number of unstable terminal groups that affect the molding die and thus is suitably used for injection molding.

[0046] The resulting injection molded article can be suitably molded into a hollow shape such as a tube, bottle, joint, valve, pipe, and the like, but is not limited thereto.

[0047] The injection molded article made of the heat-meltable fluororesin of the present invention is free from thermal decomposition of the resin due toAP0444-W001low-temperature molding, and has a well-balanced combination of excellent mechanical strength (toughness), flex resistance, solvent resistance, and the like, and is therefore particularly suitable for use in semiconductor manufacturing processes, chemical plants, and the like.EXAMPLES

[0048] The present invention is described below in further detail by presenting examples and comparative examples, but the present invention is not limited to these examples.

[0049] The measurement methods of the physical properties and the raw materials that are used in the present invention are as shown below.A. Measurement of physical properties(1) MFR

[0050] Using a corrosive-resistant melt indexer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) equipped with a cylinder, orifice, and piston in accordance with ASTM D 1238, 5 g of the sample was filled into the cylinder maintained at 372 ± 1°C for five minutes, then extruded through an orifice under a 5 kg load (piston and weight), after which the amount of the melt extruded at this time per 10 minutes (g / 10 min) was determined as the MFR. (2) Amount of TFE units and PEVE units

[0051] A calibration curve for the amount of PEVE was obtained by a calibration curve method using a sample with a known amount of PEVE of about 50 pm and a ratio of absorbance at 9.17 pm to absorbance at 4.25 pm, the presence of PEVE being confirmed in an infrared band at 9.17 pm using an absorption band at 4.25 pm as an internal thickness standard by means of a Fourier transformation infrared spectrophotometer (FT-IR iS50 manufactured by Thermo Fisher Scientific). Afilm having a thickness of about 50 pm obtained by melt compression molding at 350°C and then water cooling was measured for the PEVE amount in the TFE / PEVE copolymer from the calibration curve and the obtained infrared absorption spectrum according to the method described in U.S. Pat. No. 5760151.AP0444-W001(3) Number of unstable terminal groups

[0052] Using a sample having a known number of terminal groups of about 250 pm and a Fourier transformation infrared spectroscopic analyzer (FT-IR iS50 manufactured by Thermo Fisher Scientific), the absorbance of -COF 5.31 pm, -C=O(M) 5.52 pm and -C=O(D) 5.63 pm among -COOH groups, and -NH2 2.91 pm among -CONH2 groups was confirmed, and a calibration curve was prepared using a calibration curve method. The sample was melt-compression molded at 350°C, and then water-cooled to obtain a film having a thickness of 0.25 to 0.3 mm, where the number of unstable terminal groups per 106carbon atoms contained in the TFE / PEVE was determined from the calibration curve and the obtained infrared spectrum according to the method described in US Patent No. 4675380.(4) Zero shear viscosity

[0053] A sample was melt-compression molded at 350°C, and then water-cooled to obtain a film having a thickness of 1.5 mm, which was cut into a circular shape having a 25 mm diameter, and measurements were performed using a dynamic viscoelasticity measurement device (ARES manufactured by Rheometric Scientific F. E.) in a parallel plate mode at a temperature of 340°C in a frequency range of 100 to 0.1 rad / sec. The Cox-Merz rule was applied to the obtained data of the complex viscosity, and curve fitting was performed using the Cross model. The zero-shear viscosity was calculated by curve fitting using the following formula.Formula y = (C1 - C2) / (1 + (C3 * x)AC4) + C2C1 = zero shear viscosityC2 = infinite shear viscosityC3 = consistency factorC4 = shear rate indexx = frequency (rad / sec)y = shear viscosity (Pa»s)AP0444-W001The shear viscosity at x = 0 was taken from the fitted curve as the zero shear viscosity.(5) Melting point (Tm) and crystallization temperature (Tc)

[0054] A differential scanning calorimeter (DSC 8500 manufactured by PerkinElmer Inc.) was used. 10 mg of test sample was weighed and placed in a dedicated aluminum pan, crimped by a dedicated crimper, and stored in the DSC main unit, and then temperature increase was started. The temperature was raised from 150°C to 360°C at a rate of 10°C / min, held at 360°C for 3 minutes, and then lowered to 150°C at a rate of 10°C / min. The crystallization peak temperature of the crystallization curve obtained at this time was calculated as the crystallization temperature (Tc). Furthermore, the temperature of the sample was again increased from 150°C to 360°C, and the melting peak temperature was determined from the melting curve obtained at this time as the melting point (Tm).(6) Tensile properties (breaking strain, toughness)

[0055] The measurement was performed in accordance with ASTM D3307. A dumbbell test piece (parallel portion is 5 mm wide and 22 mm long) was prepared from a film having a thickness of about 1 ,5mm obtained by meltcompression molding a sample at 350°C in a molding die in accordance with ASTM D3307, measurement was performed at a chuck-to-chuck distance of 22 mm and a rate of 50 mm / min while maintaining the sample temperature at 23°C using a Tensilon manufactured by Orientec Co., Ltd.

[0056] The breaking strain represents the strain at the breaking point on the obtained stress-strain curve, and toughness represents the energy consumed up to the break and is calculated by integrating the stress-strain curve on the horizontal axis (strain).

[0057] Each measurement value was measured for five test pieces, and the average value thereof was determined.AP0444-W001(7) MIT flex life value (FL value)

[0058] The measurement was performed in accordance with JIS P8115. A test piece having a length of about 110 mm and a width of 15 mm was prepared from a film having a thickness of about 0.2 mm obtained by melt-compression molding a sample at 350°C, and the test piece was bent at an angle of 135 degrees in the right and left directions at a rate of 175 times / min under a load of 1 kg using a triple MIT folding endurance tester manufactured by Myss Shikenki Co., Ltd., and the number of times of bending until the test piece broke was determined.(8) Weight change ratio in isopropanol (I PA)

[0059] The test piece used in the aforementioned tensile property measurement was kept at 70°C for 2 weeks in a thermostat safety oven manufactured by ESPEC Corp, while maintaining a state of being completely immersed in I PA. The sample was removed from the container and dried overnight, and then the weight was measured, and the weight change rate was calculated from the weight of the sample before and after immersion in I PA. B. Raw materials(Example 1)

[0060] A dispersion of tetrafluoroethylene-perfluoroethyl vinyl ether (TFE / PEVE) copolymer was prepared by a method according to Examples 1 to 3 described in Japanese Patent No. 5,588,679, except that perfluoroethyl vinyl ether (PEVE) was used instead of perfluoropropyl vinyl ether (PPVE).

[0061] Specifically, the surfactant for aqueous emulsion polymerization was a solution (II) obtained by mixing a fluoromonoether acid (I) expressed by CF3CF2CF2OCF(CF3)COOH and a perfluoropolyether acid (PFPEA) expressed by C3F7O(CFCF3CF2O)nCFCF3COOH having a number average molecular weight of about 1500, with t-BuOH ata ratio of 1:1.5, neutralizing the mixture with aqueous ammonia, and then diluting the neutralized mixture with degassed water.

[0062] 1850 mL of deionized water was degassed by evacuation and purging with nitrogen gas in a 1 -gallon (3.8 L) reaction vessel equipped with aAP0444-W001horizontal stirring blade. 250 g of the fluoromonoether acid of the aforementioned solution (II) and 7.5 g of the fluoromonoether acid of the aforementioned formula (I) were added to a reaction vessel at atmospheric pressure to net 0.29 g of perfluoropolyether acid (PFPEA). After the stirrer was operated at 120 rpm, the temperature was raised to 85°C and ethane was fed to the reaction vessel until the pressure in the reaction vessel rose to 0.03 MPa. Furthermore, 102 g of perfluoroethyl vinyl ether (PEVE) was fed into the reaction vessel. Furthermore, the reactor was pressurized with tetrafluoroethylene (TFE) to 2.1 MPa. Then, 3.0 g / L of ammonium persulfate (APS) in 100 g of aqueous solution was fed into the reaction vessel as an initiator. After initiation of the reaction as determined by a 0.03 MPa pressure drop, 1.90 g / L of an APS aqueous solution was fed at a rate of 1.0 g / min, PEVE was fed at a rate to provide an 86 g feed rate during the polymerization, and TFE was fed to maintain the pressure at 2.10 MPa. When 948 g of TFE had been fed after the start of the reaction, all feeding and stirring was stopped. Thereafter, the reactor was degassed to obtain a dispersion of TFE / PEVE copolymer.

[0063] The obtained dispersion was stirred and aggregated to obtain an aggregate and then dried at 240°C for 15 hours to obtain a powdery TFE / PEVE copolymer. The obtained powder was extruded at 340°C using a <$>20mm single screw extruder manufactured by Tanabe Plastics Co., Ltd., and pelletized using a strand cutter. The pellets thus obtained were treated with fluorine gas by the method described in Japanese Unexamined Patent Application S62 -104822 to stabilize (fluorinate) the terminal groups.(Example 2)

[0064] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that 110 g of PEVE was added before TFE was fed to the reaction vessel, and 94 g of PEVE was fed during polymerization.AP0444-W001(Example 3)

[0065] Polymerization, coagulation, extrusion, and fluorination were performed in the same manner as in Example 1 , except that 115 g of PEVE was added before feeding TFE to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.28g / L, and 98 g of PEVE was fed during polymerization.(Example 4)

[0066] Polymerization, coagulation, extrusion, and fluorination were performed in the same manner as in Example 1 , except that the stirring rate of the stirrer was 110 rpm, 110 g of PEVE was added before feeding TFE to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.75 g / L, the concentration of the aqueous APS solution fed during polymerization was 1 .80g / L, and 94 g of PEVE was fed during polymerization.(Comparative Example 1)

[0067] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was 115 rpm, the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, and the concentration of the aqueous APS solution fed during polymerization was 1 ,28g / L.(Comparative Example 2)

[0068] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, and the concentration of the aqueous APS solution fed during polymerization was 1.28g / L.AP0444-W001(Comparative Example 3)

[0069] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was 125 rpm, 132 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.28g / L, and the amount of PEVE fed was 112 g- (Comparative Example 4)

[0070] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was 125 rpm, 116 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.75 g / L, the concentration of the aqueous APS solution fed during polymerization was 1 .75g / L, and the amount of PEVE fed was 99 g. (Comparative Example 5)

[0071] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 105 rpm, 94 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 80 g.(Comparative Example 6)

[0072] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was 110 rpm, 140 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 3.25 g / L, the concentration of the aqueous APS solution fed during polymerization was2.1g / L, and the amount of PEVE fed was 120 g.AP0444-W001(Comparative Example 7)

[0073] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1, except that the stirring rate of the stirrer was 115 rpm, 140 g of PEVE was added before TFE was fed to the reaction vessel, the concentration of the APS aqueous solution before the start of polymerization was 2.0 g / L, the concentration of the aqueous APS solution fed during polymerization was 1.28g / L, and the amount of PEVE fed was 120 g- (Comparative Example 8)

[0074] Polymerization, coagulation, extrusion and fluorination were carried out in the same manner as in Example 1 , except that the stirring speed of the stirrer was changed to 105 rpm, 125 g of PEVE was added before TFE was supplied to the reaction vessel, and the amount of PEVE supplied during polymerization was changed to 105 g.Table 1< < < <<<<<<<<<AP0444-W001Table 1 (Continued)

Claims

AP0444-W001Claims1. A heat-meltable fluororesin for injection molding, comprising:a copolymer containing 88.7 mass% or more and less than 90.9 mass% of tetrafluoroethylene (TFE) and more than 9.1 mass% and no more than 11.3 mass% of perfluoro(ethyl vinyl ether) (PEVE),wherein the melt flow rate at 372°C is in a range of 25 to 50g / 10 min; and the number of unstable terminal groups per 1 x 106carbon atoms in the copolymer is 50 or less.

2. The heat-meltable fluororesin for injection molding according to claim 1 , having a melting point of 280°C or lower and a crystallization temperature of 260°C or lower, as measured by a differential scanning calorimeter.

3. An injection molded article, comprising the heat-meltable fluororesin for injection molding according to claim 1 or 2.

4. The injection molded article according to claim 3, which is any one of a tube, a bottle, a joint, a valve, or a pipe.

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